Thermal relay



July 3, 1928. 1,675,370

F. H. MILLER THERMAL RELAY Original Filed June 9. 1920 77 JV 'ATTORNEYtorque may be developed therein.

Patented July 3, 1928.

UNITED STATES PATENT OFFICE.

FREDERICK H. MILLER, QF VTILKINSBURG, PENNSYLVANIA, ASSIGNOR T0v\VILQCPIBTG- HOUSE ELECTRIC & MANUFACTURING GOMRANY, A CORPORATION, OFPENNSYI VANIA.

THERMAL RELAY.

Continuation or application Serial No. 387,571, filed, Janet), 1920.lhis application filed March 12, 1925.

, Serial No. 14,963.

My invention relates to electrical proteca tive devices and particularlyto thermal relays. i

athermal relay that shall have sufiicient time interval in the operationthereof to efiect protection of electrical apparatus from overloads.

Another" object "or my invention is to provide a relay, of theabove-indicated character,.that shall employ abimetalhc element of suchshape that a .relativelylarge quantity of heat, and, consequently,a'relatively large Another object of my invention is to pro vide a relayof the above-indicated character, that shall be simple and economical inconstruction'and'reliable in operation.

Heretofore, considerable diiiiculty 'has been encountered in developingsuflicient heat in a small bimetallic element to obtain. a torque of therequired value'be'cause the resistance of the element was too small tocause a heat loss therein of suflicient value to develop the requiredtorque.

In view of this difliculty of developing sui'ficient heat in abimetallic element, I provide an element that corresponds in size tothat previously employed but so slotted as to embody acurrent-conducting path greatly exceeding in length the originalcurrentconducting path of the element. of the slotting of the element,not only is the length of the current-conductingpat-h greatly increasedbut the cross-sectional area of the conducting path is so decreased thatthe efiective resistance of the element is greatly multiplied. The heatlosses and, consequently, the torque developed, are correspondinglyincreased.

Figure 1 of the accompanying drawings is a diagrammatic view of anelectric circuit embodying my invention.

Fig. 2 is a perspective view of the bimetallic element employed in thedevice shown in Fi 1.

liig. 3 is an end view, partially in elevation and partially in section,of the bimetallic element shown in Fig. 2.

An electrical apparatus 1 is adapted to receive energy from a circuit 2through a circuit interrupter 3 and is provided with a thermal relay 4to permit the interrupter 3 By reason to open when the temperature ofthe apparatus 1 attains or exceeds a predetermined v v I j dangerousvalue. The interrupter 3 is pro- One object of my invention is toprovide vided with a. holding electromagnet 5 and a restraining spring 6that is adapted to open the interrupter '3 when the holding magnet5'becomes de-energized.

The relay 4 comprises a cylindrical casing 7 that has two ferrules 8 and9 mounted on the respective ends thereof. A supporting member 10 issupported, at one end, by a screw 11 that extends through the ferrule 8,and at the other end, by a supporting member 12 that is mounted on aninsulating block 13 by means of a screw 14. The insulated block 13 isdisposed within the ferrule 9 adjacent to the-end thereof, and thescrew'14 is so accessible as to readily permit the connection of an externalconductor thereto. A contact member 15 is also mounted on the supportingmember 12 and is adapted to be engaged by a movable contact member 16that is supported by a bimetallic element 17. The bimetallic element 17is composed of two metals having unequal coefficients of expansion. Oneend of the bimetallic element 17 is so mounted on the supporting member10 as to be in electrical engagement therewith, and the other end of theelement is electrically connected to the ferrule 9 by means of aflexible conductor 18. A supporting member 19, of flexible insulatingmaterial, is disposed along one side of the bimetallic element 17 and issecured thereto by a plurality of rivets 20, or some similar means, andserves to maintain the bimetallic element substantially rigid. Themovable contact member 16 is secured to the movable end of thebimetallic member 17 and is in electrical engagement therewith.

As current traverses the circuit to energize, or to actuate, theapparatus 1, the bimetallic element 17 of the relay 4 serves as aconductor between the ferrule 8 and the ferrule 9, in connection withthe flexible conductor 18, and is, therefore, heated in accordance withthe heating of the apparatus 1 by the current passing therethrough. As.

' the contact member 16 to be disengaged from the contact member 15.

By so constructing the bimetallic element 17 that the resistance thereofis of the correct value to generate a predetermined amount of heattherein in accordance with the temperature rise of an electrictranslating device to f be protected and that the combined heatstoragecapacity vof said element and of the cylindrical casing 7 is of thecorrect value, the relay 4: may be caused to function in accordance withthe'thermal characteristics of thejele'ctric translating devicewithwhich'it may be in circuit. 7

The circuit'of the electromagnet 5, which is normally completed throughthe contact members '15 and 16, is opened upon] the disengagementof thecontact members. The

electromagnet 5 is thereupon de-energized',

and the circuitinterrupter 3 is, consequently, opened by the restrainingspring 6;

"lVhen current ceases to traverse the element 17 the temperature thereofdecreases, andiengagement between the contact members 15 and'16 isre-established.

It will be understood that the main teature of my invention is toincrease the inherent heating capacity of a bimetallic element to permitthe use of a relatively stifi element to obtain protection when theelement is traversed by relatively low values of current without the useof external heating means.

Although I have shown one form of relay embodying a slotted bimetallicelement, I do not limit therelement to the particular mode of slottingthat is illustrated, or to a relay embodying an element having theparticulararrangement that is illustrated, as various modifications maybe made therein within the spirit and scope of the invention as setforth in 'the appended claims. I claim as my invention:

1, A thermal element comprising a 'bimetallic strip having a'pluralityof laterally extending slots, said slots being alternately open atopposite edges thereof to increase the length of the current-conductingpath,

therethrough, and means for controlling the relative movement betweenthe different portions so constituted.

' 2'. A thermal element comprising a. bi-

metallic strip having a'plurality ofzlateralv tions relatively movablewith respect to each 7 other, and means whereby said portions are causedto cooperate to eflect a predetermined operation of the bimetallicelement as a whole. 7 V I In testimony whereof, I have hereuntosubscribed myname this 11th day of March,

1925. i V t V FREDERICK H. MILLER.

